The present invention relates to a regulator valve for a hydraulic anti-skid apparatus for installation in a vehicle braking system between a master cylinder and a wheel brake cylinder to prevent the road wheels from locking in braking operation, and more particularly to a regulator valve arranged to control a hydraulic power pressure applied to the anti-skid apparatus from a hydraulic power pressure source in response to a master cylinder pressure from the master cylinder.
Such a conventional hydraulic anti-skid apparatus as described above includes a cut-off valve disposed within a braking circuit connecting a master cylinder to rear wheel brake cylinders, a bypass valve disposed within a bypass passage or circuit of the braking circuit, and first and second differential pistons respectively arranged to control opening and closing operations of the cut-off valve and the bypass valve. The first differential piston is applied at its small diameter portion with a master cylinder pressure from the master cylinder and at its large diameter portion with a hydraulic power pressure from a hydraulic power pressure source in the form of a fluid pump by way of a solenoid valve. The solenoid valve is arranged to apply the hydraulic power pressure to the large diameter portion of the first differential piston under its deenergized condition. When energized in response to an electric signal from a computer in connection to a wheel lock sensor, the solenoid valve acts to connect the large diameter portion of the first differential piston to a fluid reservoir. Thus, the first differential piston acts to normally open the cut-off valve during deenergization of the solenoid valve. When connected to the fluid reservoir in response to energization of the solenoid valve, the first differential piston is displaced by the master cylinder pressure to close the cut-off valve and subsequently to increase a capacity downstream the cut-off valve thereby to decrease the pressure in the rear wheel brake cylinders.
The second differential piston is applied at its small diameter portion with the master cylinder pressure and at its large diameter portion with the hydraulic power pressure directly. Thus, the second differential piston acts to normally close the bypass valve under the hydraulic power pressure applied thereto and to permit the flow of fluid from the master cylinder to the rear wheel brake cylinders through the cut-off valve. When the hydraulic power pressure decreases below a predetermined value due to damage of the fluid pump, the second differential piston is displaced by the master cylinder pressure to open the bypass valve so as to directly apply the master cylinder pressure to the rear wheel brake cylinders. In the above-described arrangement, it is required to maintain the hydraulic power pressure at a relatively high value under inoperative condition of the master cylinder in order to avoid an error in operation of the bypass valve due to delay of increase of the hydraulic power pressure relative to increase of the master cylinder pressure. This results in fuel consumption in operation of a prime mover of the vehicle and results in decrease of durability of sealing members assembled within the anti-skid apparatus.